Rotary furnaces are commonly employed during the smelting of lead. In such a furnace, a source of lead (e.g., free lead, lead cake, ore, etc.) is added to the rotary furnace along with soda ash, coke, and an iron flux material. Within the furnace, the lead is smelted, and the remainder of the ingredients are produced as slag. Such slag contains mostly iron and sodium compounds, especially oxides, hydroxides, and sulfides of iron and sodium. Rotary slag also often contains trace amounts of heavy metal contamination, especially lead, but also other heavy metals.
Currently, rotary slag is disposed of as industrial waste, generally in a landfill. Disposal of waste in landfills consumes ever dwindling landfill space and also requires considerable transportation costs. Moreover, landfilling rotary slag requires extensive treatment at the landfill site. For example, largely because of the heavy metals often present in rotary slag, it first must be fixed, typically by admixture with concrete and other additives. Such treatment requires considerable space and resources.
Aside from the expense and environmental threat associated with landfilling rotary slag, current industrial practice also presents other inefficiencies. Typically, iron flux material is supplied in the form of mill scale, which generally is purchased and added to the rotary furnace each time lead is smelted. Moreover, as mentioned, rather than being smelted, some of the lead is lost as waste in the rotary slag.
Thus, current lead smelting methods using a rotary furnace consume valuable resources and require considerable expense to avoid environmental pollution. In view of these problems, there exists a need for a method for treating rotary slag.